Make sure your character is standing upright in the preview, and everything looks alright. Mixamo will show you a preview of your character after uploading the. Once you log in to Mixamo, you can easily spot the upload character button. You can even use some free character models that are available in Mixamo itself.
However, you can go ahead and upload any character. Characters and Animation Options Available in Mixamo Uploading Your Character to Mixamo You only need to have an Adobe account to use Mixamp.
